The present invention relates to an image processor designed for either image enlargement processing or image reduction processing or the both or contour correction.
It is a common practice for conventional image processors to execute the image processing in the order of the contour correction to input video signal and subsequent image enlargement processing and/or image reduction processing, or in the order of the image enlargement processing and/or image reduction processing and subsequent contour correction.
In other words, the contour correction is not correlated with the image enlargement processing and/or image reduction processing.
Further, as discussed above, in a conventional image processor, the contour correction is not correlated with the image enlargement processing and/or image reduction processing, causing a problem such as very poor contour correction effect or unnecessary contour emphasis.
For instance, in a system designed for making the contour correction subsequently to the image enlargement processing to the input video signal, the contour correction is made to the video signal subsequently to the image enlargement processing, causing a problem such as making unnecessary emphasizing of contour.
Further, in a system designed for executing the image reduction processing subsequently to the image reduction processing for input video signal, the band of the high-pass frequency component intensified by the contour emphasizing is limited in the stage of image reduction processing, thereby causing a problem that very poor contour correction effect results.
The present invention is made in consideration of the above problems and is designed to provide an image processor that is not only capable of freely selecting either the image enlargement processing or image reduction processing but also capable of making appropriate contour correction regardless of whether the image enlargement processing or image reduction processing is selected.
The image processor according to the present invention comprises a coefficient memory for previously storing the coefficients for image enlargement and image reduction, a coefficient read-out controller for reading out corresponding coefficient from the coefficient memory according to enlargement/reduction selection signal, a characteristic variable filter for executing the filter processing corresponding to either image enlargement or image reduction according to the coefficient data read out by the coefficient read-out controller, an image memory and a contour correction circuit and selector groups, the selector groups being respectively provided in the preceding and subsequent stages of each of the image memory, the contour correction circuit and the characteristic variable filter and connected to one another.
When the image enlargement processing is selected by the enlargement/reduction selection signal, the selector groups makes the input video signal being processed sequentially through the contour selection circuit, image memory and characteristic variable filter, while the video signal is made to be processed sequentially through the characteristic variable filter, image memory and contour correction circuit when the enlargement/reduction selection signal for image reduction processing is selected.
When the image enlargement processing is selected, the input video signal is made to be processed sequentially through the contour correction circuit, image memory and characteristic variable filter. In this case, the characteristic variable filter executes the filter processing for image enlargement according to the coefficient data read out from the coefficient memory in response to the enlargement/reduction selection signal. In this case, since the image enlargement processing is executed after the contour correction, unnecessary emphasizing of contour can be prevented unlike the case of the conventional system wherein the contour correction processing is applied to the video signal which has already undergone the image enlargement processing.
When the image reduction processing is selected, the input video signal is processed sequentially through the characteristic variable filter, image memory and the contour correction circuit. In this case, the characteristic variable filter executes the filter processing for image reduction according to the coefficient data for the image reduction read out from the coefficient memory in response to the enlargement/reduction selection signal. In this case, since the contour correction is made after the image reduction processing, the band of the high-pass frequency component will not be limited for the image reduction processing unlike the case of the conventional system.
Further, in the image processor according to the present invention, the coefficient memory previously stores the coefficient data for image enlargement and image reduction in horizontal direction and vertical direction respectively; the coefficient read-out controller reads out the corresponding coefficient data from the coefficient memory according to the enlargement/reduction selection signal for selecting either image enlargement processing or image reduction processing with respect to each of the horizontal direction and vertical direction; the characteristic variable filter comprises a horizontal characteristic variable filter, for executing the filter processing for either the image enlargement processing or image reduction processing in horizontal direction according to the coefficient data for horizontal direction read out by the coefficient read-out controller, and a vertical characteristic variable filter for executing the filter processing for either the image enlargement processing or image reduction processing in vertical direction according to the coefficient data for vertical direction read out by the coefficient read-out controller.
With the arrangement described above, either the image enlargement processing or image reduction processing, each with respect to either horizontal direction (transverse direction) or vertical direction (perpendicular direction) can be selected freely.
In the image processor according to the present invention, when the vertical reduction and horizontal reduction are selected by the selector groups, processing proceeds sequentially through the horizontal characteristic variable filter, vertical characteristic variable filter, image memory and contour correction circuit; when the vertical reduction and horizontal enlargement are selected, the processing proceeds sequentially through the vertical characteristic variable filter, image memory, horizontal characteristic variable filter and contour correction circuit; when vertical enlargement and horizontal reduction are selected, the processing proceeds sequentially through the horizontal characteristic variable filter, image memory, vertical characteristic variable filter and contour correction circuit; when the vertical enlargement and horizontal enlargement are selected, the processing proceeds sequentially through the contour correction circuit, image memory, horizontal characteristic variable filter and vertical characteristic variable filter.
With the arrangement described above, when the image enlargement processing or image reduction processing is selected, each with respect to both the horizontal and vertical directions, not only the appropriate contour correction can be accomplished but also it can be prevented that the contour correction effect becomes ineffective when the image enlargement processing in vertical direction is selected while the image reduction processing in horizontal direction is selected and vice versa.
Further, in the image processor according to the present invention, when the vertical reduction and horizontal reduction are selected by the selector groups, the processing proceeds sequentially through the horizontal characteristic variable filter, vertical characteristic variable filter, image memory and contour correction circuit; when vertical reduction and horizontal enlargement are selected, the processing proceeds sequentially through the contour correction circuit, vertical characteristic variable filter, image memory and horizontal characteristic variable filter; when vertical enlargement and horizontal reduction are selected, the processing proceeds sequentially through the contour correction circuit, horizontal characteristic variable filter, image memory and vertical characteristic variable filter; when vertical enlargement and horizontal enlargement are selected, the processing proceeds sequentially through the contour correction circuit, image memory, horizontal characteristic variable filter and vertical characteristic variable filter.
With the arrangement described above, when the image enlargement processing or image reduction processing is selected with respect to both the horizontal and vertical directions, not only appropriate contour correction can be accomplished but also unnecessary emphasizing can be prevented when image enlargement in horizontal direction is selected while image reduction in vertical direction is selected and vise versa.
Further, in the image processor according to the present invention, the contour correction circuit comprises a horizontal contour sampler for sampling the contour component in horizontal direction, a vertical contour sampler for sampling the contour component in vertical direction, a first adder for adding the contour component sampled by the horizontal contour sampler and the contour component sampled by the vertical contour sampler and a second adder for adding the contour component outputted from the first adder to the video signal to be inputted to the contour correction circuit to output the video signal corrected for contour.
With the arrangement described above, the contour can be corrected by sampling and adding the contour components in horizontal direction and vertical direction.